Britain's Sky News and The Sun, Daily Express and Daily Telegraph newspapers are reporting that two of the men arrested were hospital doctors. Police have refused to comment on the claim.
Separately, a realtor in Glasgow is reporting that police were police were on the trail of the Glasgow airport bomb suspects minutes before the attack.
Daniel Gardiner of the Let-It agency said officers had contacted his company after tracking phone records linked to the foiled London car bomb attacks.
He says police left a card at the home of a colleague on Saturday, asking him to get in touch with authorities.
"The card was put through prior to the incident at Glasgow Airport," says Gardiner, adding that police were interested in the tenant who had taken a six-month lease on a house.
Police on Sunday searched a property rented by Gardiner's company in Houston, near Glasgow Airport. Gardiner says police interviewed staff at the Let-It office and took away all documentation about the tenant.
British Prime Minister Gordon Brown said "it is clear that we are dealing, in general terms, with people who are associated with al Qaeda." He warned Britons that the threat would be "long-term and sustained" but said the country would not be cowed by the plot targeting central London and Glasgow's airport.
"We will not yield, we will not be intimidated and we will not allow anyone to undermine our British way of life," he said in a nationally televised interview.
A British government security official said a loose U.K.-wide network appeared to be behind the attacks but investigators were struggling to pin down suspects' identities — even two arrested after they drove a Jeep Cherokee into Glasgow's main airport terminal Saturday and set it ablaze.
"These are not the type of people who always carry identity documents, or who use their real identities," the official said on condition of anonymity because of the sensitivity of the inquiries. "Very little has been gleaned so far from the biological data."
He said police and MI5, the internal security agency, did not know if the suspects were British born, from overseas, or some combination of the two, despite local media reports that they were not from Britain. Officials released few other details of the investigation.
Two men rammed the jeep into the airport entrance, shattering the glass doors and igniting a raging fire. One of the suspects, his body in flames after the attack, was taken to the nearby Royal Alexandra Hospital, where police on Sunday carried out a controlled explosion on a vehicle they said also could be linked to the plot.
On Friday, authorities thwarted coordinated bomb attacks in central London after an ambulance crew outside a nightclub spotted smoke coming from a Mercedes that turned out to be rigged with gasoline, gas canisters and nails. A second Mercedes filled with explosives was found hours later in an impound lot, where it was towed for parking illegally.
"We are learning a great deal about the people involved in the attacks here in Glasgow and in the attempted attacks in central London. The links between them are becoming ever clearer," Peter Clarke, head of Scotland Yard's counterterrorist unit, said in Scotland.
"I'm confident, absolutely confident, that in the coming days and weeks we will be able to gain a thorough understanding of the methods used by the terrorists, the way in which they planned their attacks and the network to which they belong."
Britain raised its terror alert to "critical" — the highest possible level — and the U.S. homeland security chief, Michael Chertoff, said Sunday that air marshals would be added to overseas flights.
"Al Qaeda has imported the tactics of Baghdad and Bali to the streets of the U.K.," said Lord Stevens, Brown's terrorism adviser, referring to the 2002 and 2005 attacks on the Indonesian resort island that killed more than 200 people and the daily car bombings in the Iraqi capital.
Glasgow Airport Attack
on Saturday, shattering glass doors and stopping within yards of where holidaymakers were lined up at check-in counters. The two people inside the car were arrested — one of them on fire.
Police arrested two people – a 26-year-old man and a 27-year-old woman – on a major highway in Cheshire in a joint swoop by officers from London and Birmingham.
A fifth suspect, a 26-year-old man, was arrested in Liverpool, and two homes were being searched there, police said.
Officers also searched a residential area about a mile from Glasgow's airport and, at the Royal Alexandra Hospital, carried out a controlled explosion on the suspicious vehicle.
"It is believed that this car is connected to yesterday's incident at Glasgow International Airport," Strathclyde Police said in a statement. Police said no explosives were found, but gave no other details.
On the street where the house was searched, police had set up a tent and trailer to work out of, and officers carried crates of evidence out of the building into the night.
CBS News correspondent Sheila MacVicar reports that neighbors said a house being searched was rented a month ago to two Asian men.
In Saturday's attack, the green Jeep barreled toward Glasgow's main airport terminal at full speed shortly after 3 p.m., hitting security barriers before crashing into the glass doors and exploding, witnesses said.
Police wrestled the driver and a passenger, both described by witnesses as South Asian, to the ground, arresting them and taking one to the hospital. Witnesses said one of the men was engulfed in flames and spoke "gibberish" as an official used a fire extinguisher to douse the fire.
London Car Bomb Investigation
after two potential car bombs were found on Friday.
Two Mercedes loaded with gasoline, gas canisters and nails were found abandoned Friday in what police believe was an attempt to kill scores or even hundreds of people. Detectives said they were keeping an open mind about the perpetrators, but terrorism experts said the signs pointed to an al Qaeda-linked or inspired cell.
CBS News has learned the police have been able to reconstruct the journey of the bomb vehicles through London using closed-circuit TV images.
And using license plate recognition technology, the police now know precisely where and when the bombers brought their cars into central London.
Those video cameras are sophisticated and sensitive at night. Sources say there are good quality images of both drivers. CBS News has learned that the police know the identity of at least one of the suspects.
Intelligence officials were examining a post to an Islamist Web site — published hours before the cars were found, as first reported by CBS News — that suggested Britain would be attacked for awarding a knighthood to the novelist Salman Rushdie and for intervening in Muslim countries.
U.S. Airport Security Tightened
originating in Britain and Europe, the homeland security chief said Sunday.
The Bush administration said it was satisfied with its current terrorism alert level following an attack at a Scottish airport and two foiled car bombs in London.
"I think given what we know now, we're comfortable that we're at the right posture," Michael Chertoff said.
"At this moment we don't have a specific credible threat against the United States," he said.
U.S. airports and mass transit systems are tightening security ahead of the Fourth of July holiday and more air marshals will travel on overseas flights.
"Going forward, we will be doing some enhanced air marshal work and similar types of activities with respect to U.K. travel," Chertoff said.
Muslims Worry About Backlash
on Sunday after three failed bomb attacks in London and Glasgow. Government and religious leaders appealed for calm, but some Muslims braced for a backlash — while some non-Muslims looked for someone to blame.
The attacks sparked scattered incidents of racist abuse on the streets of London, with young white men targeting Muslim taxi drivers and others of South Asian appearance. Glasgow lawmaker Mohammad Sarwar said some Muslims in Scotland had been threatened or targeted with abusive graffiti.
— but also at a society some felt singles Muslims out for scrutiny whenever there is a terrorist attack.
"We are seething with anger about this," said Osama Saeed, Scottish spokesman for the Muslim Association of Britain.
"As a community not only are we just as likely to be victims as anyone else, but we are also looked to in order to provide direction and in some respects take responsibility for this," he added.